A nuclease from a marine Alteromonas bacterial strain is to be further characterized with respect to its physical properties and enzyme kinetic properties while acting on a variety of nucleic acid substrates. Studies which have shown that the nuclease can cause the cleavage of DNA helix at the sites of covalent alteration of the helix caused by chemical agents which are known to be carcinogens and/or mutagens will be extended to more compounds, and the detailed kinetics of the enzyme action with regard to certain types of lesions in duplex DNA structure will be determined. Attempts to use the nuclease, in conjunction with the metabolic activation of procarcinogens and/or promutagens by crude preparations of liver microsomes, to detect damage in duplex DNA caused by the metabolically activated compounds will be carried out. An extensive series of studies to characterize kinetically the exonucleolytic degradation of duplex nucleic acids caused by this nuclease is planned. Experiments have further been designed to use this enzyme in the quantitation of the equivalent single-strand content of covalently closed circular duplex DNAs having varying numbers of superhelical turns per unit molecular weight. Studies are anticipated which should demonstrate the use of the Alteromonas nuclease in the removal of the non-base-paired regions from heteroduplex DNA. Spectrophotometry, gel electrophoresis, and preparative and analytical ultracentrifugation are the major techniques which will be used in this work.